The present invention relates generally to hybrid motor vehicles and, more particularly, to a hybrid automatic transmission adapted for installation in the drivetrain of a hybrid motor vehicle.
Automobile manufacturers are constantly working to improve fuel efficiency. Improvements in fuel efficiency are typically directed to reduced weight, improved aerodynamics, and reduced power losses through the powertrain. However, the need to improve fuel efficiency is commonly offset by the need to provide enhanced comfort and convenience to the vehicle operator. As an example, manually-shifted transmissions are more fuel efficient than automatic transmissions due to lower parasitic losses. The higher losses associated with conventional automatic transmissions originate in the torque converter, the plate clutches and the hydraulic pump used to control the hydraulic shift system. However, a vast majority of domestic passenger vehicles are equipped with automatic transmissions due to the increased operator convenience they provide. Recent advances in power-operated shift systems have allowed development of xe2x80x9cautomatedxe2x80x9d versions of manual transmissions which automatically shift between sequential gear ratios without any input from the vehicle operator. Thus, automated manual transmissions provide the convenience of a traditional automatic transmission with the efficiency of a manual transmission.
Automobile manufacturers are also actively working to develop alternative powertrain systems in an effort to reduce the level of pollutants exhausted into the air by conventional powertrains equipped with internal combustion engines. Significant development efforts have been directed to electric and fuel-cell vehicles. Unfortunately, these alternative powertrain systems suffer from several disadvantages and, for all practical purposes, are still under development. However, several different xe2x80x9chybridxe2x80x9d electric vehicles have recently been offered for sale. These hybrid vehicles are equipped with an internal combustion engine and an electric motor that can be operated independently or in combination to provide motive power to the vehicle.
There are two types of hybrid vehicles, namely, series hybrid and parallel hybrid. In a series hybrid vehicle, power is delivered to the wheels by the electric motor which draws electrical energy from the battery. The engine is used in series hybrid vehicles to drive a generator which supplies power directly to the electric motor or charges the battery when the state of charge falls below a predetermined value. In parallel hybrid vehicles, the electric motor and the engine can be operated independently or in combination pursuant to the running conditions of the vehicle. Typically, the control strategy for such parallel hybrid vehicles utilized a low-load mode where only the electric motor is used to drive the vehicle, a high-load mode where only the engine is used to drive the vehicle, and an intermediate assist mode where the engine and electric motor are both used to drive the vehicle, and an intermediate assist mode where the engine and electric motor are both used to drive the vehicle. Regardless of the type of hybrid drive system used, hybrid vehicles are highly modified versions of conventional vehicles that are expensive due to the componentry, required control systems, and specialized packaging requirements. Thus, a need exists to develop hybrid powertrains for use in vehicles that utilize many conventional powertrain components so as to minimize specialized packaging and reduce cost.
It is therefore an object of the present invention to provide a parallel-type hybrid powertrain or drive system for a motor vehicle.
In accordance with this object, the hybrid drive system of the present invention includes a hybrid automatic transmission that can be installed in place of a conventional transmission between the engine and the driveline of the motor vehicle.
As a related object, the hybrid automatic transmission of the present invention includes a multi-speed gearbox, an automated shift system, and an electric motor. The electric motor is operably controlled to drive the multi-speed gearbox and to provide a speed synchronization function during gear shifting.
These and other objects are provided by a multi-speed transmission having an input shaft driven by the engine, an output shaft connected to the driveline, an electric motor, a planetary geartrain driven by one or both of the engine and the electric motor, a plurality of power-operated clutches operable for selectively engaging components of the planetary geartrain, and a control system for controlling automated operation of the power-operated clutches and coordinated actuation of the engine and the electric motor.